The present invention relates generally to a turning device for turbine-machines.
Rotating machines which are shut down, especially turbines, and that require a relatively long period of time after shut down to cool off, must be kept slowly rotating in order to prevent any warping of the shaft. Furthermore, the re-starting of large turbines requires that the inertia of the shaft be overcome preferably in a manner which insures a smooth start up of the rotor. Various auxiliary turning systems are being employed both for the continuous rotation of the rotor after shut-down as well as for the start-up of the turbine.
In the case of small and medium-sized turbine-units, turning gears having pinions have been used, with turning-gear pinion arranged non-symmetrically with respect to the longitudinal axis of the turbine shaft (see especially publication 7002 by "BHS-Getriebetechnik"). Such a known arrangement has the disadvantage, however, that the gearing must be cut in and engaged manually when the turbine-unit is at a standstill. Furthermore, during a reverse rotation of the turbine-units such as during use as a compressor and as pump drives and also when the compressor and the turbine coupled to it are driven in reverse, for example, due to a counterflow of compresssed air or gases, the gearing of the known arrangements will also run backward and likely become damaged in the process.
It is a particular object of the present invention to provide a turning device which permits both a forward as well as a reverse rotation of the turbine-unit so that the turning device can be used in various systems, for example for both compressor and pump drives, without any damage to the turning gear and pinion arrangement.
The present invention solves the problems described above in that a hydraulic piston causes a turning-gear pinion that is arranged at a cam to engage a toothed ring arranged at the shaft to be turned. The cam carries a catch, into which catch a pressure cylinder is locked, thereby keeping the cam and the turning gear pinion in an engaged position. Additional devices are provided at the cam to hold the turning-gear pinion in a swing-out position. It is advantageous if the cam has a smaller radius at one side of the catch, and a larger radius at an opposite side of the catch so that the swing-out of the turning-gear pinion during a forward movement of the turbine shaft requires a relatively smaller release force. The swingout of the turning-gear pinion during a reverse movement of the turbine shaft will accordingly require a relatively greater release force. A spring-loaded leg is preferably hinged to the cam in order to hold the turning-gear pinion in place.
The rotary axis of the turning gear pinion is preferably arranged so as to lie within a line extending between the two turning points of the turbine shaft and of the cam. The cam is held in the position of engagement with the toothed ring of the turbine shaft both by a spring-loaded pressure cylinder which engages the asymmetrically formed catch of the cam, and also by a spring-loaded leg extending along the rotational axis of the cam. Accordingly, the pinion will be able to swing out toward either side. The asymmetric form of the catch for the pressure cylinder, which is due to the fact that the cam has dissimilar radii on either side of the catch, has the result that a smaller release force will be required for swinging the turning-gear pinion in the forward direction of rotation of the turbine shaft while a greater release force must be used for swinging the pinion in a direction against the normal direction of rotation, for example when the direction of the turbine shaft is reversed. The cam will thus also perform a safety function since when the torque during the start-up becomes excessive, or when the turbine shaft is turning backward, the turning-gear pinion, actuated by the cam, will become disengaged.
The turning device of the present invention can be further improved by actuating the device by a hydraulic piston in such a manner that the hydraulic piston will move the cam only into a position of engagement with the turning-gear pinion. The pinion is then held in the engaged position by the spring-loaded cylinder.